13 



COMMttN 

 DOLPHIN 



taken on Charles H. 



Figure 15,--Longline catches 



Gilbert cruise 63, by species and zone. (Zone 

 A, North Pacific Central Water; Zone B, transi- 

 tion; Zone C, North Pacific Equatorial Water.) 



Several Studies were completed recently on the distribution 

 of certain plankton organisms that could be used as indicators 

 of water masses and water types. Studies of pontellid cope- 

 pods indicated that some species have variable distributions 

 within the South Pacific study area, some occur only in the 

 proximity of land, and others are abundant only in areas char- 

 acterized by particular water masses. 



then the Hawaiian Islands. Ocean regions between island 

 groups had a much lower density of sightings than island areas. 



During our continuing study of larval tunas we noted and 

 described the unique shape of the elongate first haemal spine 

 in albacore. The study showed conclusively that albacore is 

 the only species of tuna having an enlarged, flattened haemal 

 spine on the first caudal vertebra; this characteristic is de- 

 finitive in differentiating both juvenile and adult albacore from 

 other tuna species. 



18° 19° 20° 



\ORTH LATITIDE 



Figure 16. — Surface isotherm along longitude 150° W. 

 during the period January 13 to February 15, 1963 

 ( Charles H^. Gilbert cruise 63). 



An analysis of bird flock and fish school sightings made by 

 vessels of the Biological Laboratory , Honolulu, over a 10-year 

 period clearly demonstrates a concentration of flocks and 

 schools near the island groups encompassed in the study--the 

 Hawaiian Islands, the Line Islands, and French Oceania. The 

 analysis also shows seasonal changes in density for the entire 

 area as well as variations in density between island groups. 

 The density of sighted fish schools and bird flocks appeared 

 to be greatest inFrench Oceania, followed by the Line Islands, 



Preliminary studies of skipjack stomach contents and ova- 

 ries showed that both the amount of food in the stomachs and 

 the state of maturation (female gonad index) were inversely 

 correlated with catch. 



Other recent studies concerned size, distribution, and 

 growth of skipjack; environmental factors related to catch of 

 skipjack; and the continuing analysis of catch and effort statis- 

 tics for the Hawaiian skipjack fishery. 



